Polymer supported iron complexes

The reductive dehalogenation of haloalkanes has also been achieved in high yield using polymer supported hydridoiron tetracarbonyl anion (Table 11.15). In reactions where the structure of the alkyl group is such that anionic cleavage is not favoured, carbonylation of the intermediate alkyl(hydrido)iron complex produces an aldehyde (see Chapter 8) [3]. 

A polymer-supported lipoamide-ferrous chelate system was used as catalyst for the reduction of diphenylacetylene to cis-stilbene with sodium borohydride the dithiol-iron(II) (1 1) complex formed was suggested to be the active species. The chitosanlipoamide system has the highest activity among various insoluble polymers investigated 95,96). 

Tricarbonyliron diene complexes have found many uses in synthetic chemistry but their synthesis is often not easy. Knolker has developed a range of tricarbonyl(7] -l-aza-l,3-butadiene) iron complexes that are excellent transfer agents for the Fe(CO)3 complexation of 1,3-dienes, and showed their versatility. As an extension to this work, Knolker and Gonser have prepared a polymer-supported l-aza-l,3-butadiene 321 by reaction of Merrifield s resin with phenolic l-aza-l,3-butadiene 320, formed from cinnamaldehyde and /> ra-hydroxyaniline (Scheme 105). The corresponding tricarbonyl iron complex 322 was formed by treatment of 321 with an excess of Fe2(CO)9 in THF using ultrasound. The iron complex was subsequently used efficiently as a transfer agent for the tricarbonyliron complexation of 1,3-dienes. 

Two different catalysts for hydrogen peroxide decomposition, the enzyme peroxidase (isolated from the horseradish root, HRP), and polymer-supported catalyst (acid form of poly-4-vinylpyri-dine functionalized by ferric sulfate, apFe) [99,100], are examined with an aim to compare their activity. The active center in the peroxidases is the ferric ion in protoporphyrin IX. Besides the complex made of ferric ion and protoporphyrin IX, that is ferricprotoporphyrin IX, also known as ferric heme or hemin, peroxidase possesses a long chain of proteins [101,102]. On the other hand, the macroporous acid form of polyvinyl pyridine functionalized by ferricsulfate is obtained from cross-linked polyvinyl pyridine in macroporous bead form [103]. Pyridine enables it to form coordination complexes or quaternary salts with different metal ions such as iron (111) [104]. An active center on the polymeric matrix functionalized by iron, as metallic catalyst immobilized on polymer by pyridine, has similar microenvironment conditions as active center in an enzyme [105]. 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (75). It is also a component of supported metallocene-alumoxane polymerization catalysts in the synthesis of polyethylene and polypropylene polymers (76), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (77), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (78). 

Metal-catalysts that enable the direct transfer of an Ni-moiety from chloramine-T to alkenes with moderate efficiencies include metalloporphyrinoids. For example, in 2001, Simkhovich and Gross reported that iron (IV) corrole 21 (Scheme 2.29) catalyzed olefin aziridination with chloramine-T [44]. The use of porphyrine complexes of iron [Fe(TPP)Cl] and cobalt [Co(TDClPP)] in the presence of bromamine-T also allows for aziridinating a wide variety of alkenes [45,46]. A recyclable polymer-supported manganese (II) complex, which is readily prepared from chloromethy-lated poly(styrene-divinylbenzene) (PS-DVB) in two steps, transfers an Ni unit from bromamine-T to aliphatic alkenes in a heterogeneous system [47]. 

Okada, T. et al., A comparative study of organic cobalt complex catalysts for oxygen reduction in polymer electrolyte fuel cells, J. Inorg. Organometal. Polym., 9,199,1999. Bron, M. et al., EXAFS, XPS and electrochemical studies on oxygen reduction catalysts obtained by heat treatment of iron phenanthroline complexes supported on high surface area carbon black, J. Electroanal. Chem., 535, 113, 2002. 

Further proof that cyclobutadiene liberated by ceric oxidation of the iron carbonyl complex is completely free of the metal comes from an ingenious new three-phase test for reactive intermediates which resembles the Paneth test for free radicals in its basic flow design. Thus, a cyclobutadiene-iron carbonyl complex bound to a support of polymer beads is treated as a suspension with Ce in the presence of separate polymer beads to which a trapping agent (maleimide) is bound. The resulting adduct is then liberated from the second polymer by hydrolysis for identification, its isolation... 

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